1. Field of the Invention
The present invention relates to a press molding apparatus and a press molding method, for transferring the features of a mold to a workpiece under the application of pressure.
2. Description of the Related Art
In recent years, micro-fabrication technology for press transferring fine structures on a mold to a workpiece, such as resin or metal, have been developed and become a focus of attention. This technology, called nano-imprint or nano-embossing, has a resolution on the order of several nanometers. In addition, it can mold 3D structures on a wafer by one operation. For these reasons, this technology is expected to be applicable to a wide variety of fields, such as the next-generation semiconductor fabrication, the fabrication of optical elements like photonic crystals, and the fabrication of biochips such as μ-TAS chips.
Japanese patent laid-open application No. Hei 11(1999)-033800 proposes a method of pressing a mold into a resist on a semiconductor wafer to create an imprint pattern so as to produce a pattern on the semiconductor wafer through the process of ion milling.
An article, “Uniformity in Patterns Imprinted Using Photo-Curable Liquid Polymer” by Hiroshi Hiroshima, et al, Jpn. J. Appl. Phys. Vol. 41 (2002) 4173-4177, also proposes a method in which a sapphire block is used to press a mold smaller in area than the block, and expose it to UV rays to cure UV curing resin so as to produce a pattern.
The following describes problems in the above-mentioned molding technology with reference to FIG. 5.
FIG. 5 shows a typical example of the structure of the prior art technology. A mold 106 is typically micro-fabricated on a wafer of Si or SiO2 by EB lithography, FIB, X-ray lithography, etc, or replicated by Ni electroforming. A workpiece, or work, 107 is typically an Si semiconductor wafer coated with resin, or a resin plate. The mold 106 and the work 107 are sandwiched between a mold pressing member 104 and a work pressing member 109, and pressed together by means of a press mechanism (not shown). The mold 106 and the work 107 are held typically by evacuating air (110) from grooves or holes provided in each pressing member.
In this structure, since the mold 106 is smaller in area than the mold pressing member 104, the work 107, and the work pressing member 109, the molding force is concentrated around the periphery of the mold 106 and gradually reduced to the center portion. The above-mentioned wafer is thin, with a thickness of 1 mm or less. Therefore, the uneven distribution of molding force almost directly affects the contact surface of the mold 106 and the work 107, causing an unevenness of processed depths. Further, the mold force is also reduced around the grooves or holes provided for evacuating air 110 for the same reason.
Such a structure is likely to cause stress concentration at the edges of the mold 106. The above-mentioned wafer material such as Si or SiO2 is fragile or brittle, and in many cases, a brittle fracture starts from a point of the wafer material. Further, the point at which the brittle fracture started also hastens the damage to the pressing part, increasing maintenance costs.